1. Field of the Invention
The present invention relates to the stabilization of metachromatic dyes, and compositions comprising stabilized metachromatic dyes. The present invention is also directed to processes for determining polyionic materials utilizing stabilized metachromatic dye compositions.
2. Discussion of Background Information
Colorimetry is a well-known method of chemical analysis which involves the comparison and matching of a standard color with that of an unknown color to approximate the concentration of a specific component in a sample to be analyzed. When the amount of light absorbed by a given substance in solution is proportional to the concentration of the absorbing species, colorimetry is a simple and accurate method for determining unknown concentrations. For example, if the concentration of a polymer in an aqueous system is to be determined, a sample can be taken, the absorbance of the sample in the presence of a suitable dye can then be measured and compared with a calibration curve to quickly and accurately estimate the concentration of the polymer in the aqueous system. Colorimetry provides advantageous testing since it can easily be performed at the application site.
Certain dyes undergo a unique color change upon interaction with polyionic compounds in solution known as metachromasy. Thus, metachromatic dyes are those which undergo a color change upon interaction with polyionic compounds. Any metachromatic dye can be used in a calorimetric test to determine the concentration of a substance, including polycarboxylates, sulfonates, and the like in an aqueous solution. More specifically, when anionic polymers contact a metachromatic dye, the dye molecules align with the anionic charges on the polymers, resulting in a shift in the wavelength of maximum absorbance of the dye molecule. This shift is observable as a color change in the solution containing the dye and the polymer. Thus, since polycarboxylates and sulfonates, which are anionic, induce a metachromatic change in certain dyes, their concentrations in aqueous solutions can be determined calorimetrically by measuring the absorbance, at a specified wavelength, of a solution containing polycarboxylates and/or sulfonates and a metachromatic dye and comparing this absorbance to absorbances of standards having known concentrations of the species being measured.
However, when metachromatic dyes are dissolved in aqueous solutions for use in analytical determinations, fresh samples must be prepared on a daily basis to insure accurate analysis. Aqueous solutions of metachromatic dyes are extremely susceptible to degradation due to a variety of factors, such as light, temperature, dissolved oxygen, pH, etc. For example, when pinacyanol chloride is dissolved in an aqueous solution at a concentration of 9.0xc3x9710xe2x88x925 molar, the pinacyanol chloride degrades at a rate of approximately 10 to 20% per week. Because of this degradation problem, frequent reagent preparations must be made in the field and this is not practical.
Still further, the instability of known dye solutions leads to disadvantageous results associated with the detection process. These disadvantages result in a lack of reproducibility of results, i.e., consistency of results is difficult to attain on separate days even with the same water sample.
Accordingly, there is a need to provide stable metachromatic dyes that enable simple tests for materials, particularly water treatment polymers, and especially enable simple tests that can be utilized over extended periods of time without the need for formulation in the field.
The present invention concerns methods for stabilizing metachromatic dyes so that the dyes will not be susceptible to degradation and stabilized compositions comprising the metachromatic dyes. This will ensure that any colorimetry testing using the stabilized dyes can be performed with the added assurance of reproducible results.
The present invention is directed to stabilized metachromatic dye compositions, including aqueous solutions and non-aqueous solutions of metachromatic dye, having a percent change in absorbance of less than about 10% when stored for a period of about one week, more preferably less than about 1% when stored for a period of about one week, even more preferably less than about 3% when stored for a period of about one month, even more preferably less than about 5% when stored for a period of about 3 months, even more preferably less than about 5% when stored for a period of about 6 months, even more preferably less than about 10% when stored for a period of about one year, and even more preferably less than about 5% when stored for a period of about one year.
Further, the present invention is directed to aqueous solutions of metachromatic dye comprising metachromatic dye in an aqueous solvent, the aqueous solvent having a metachromatic dye stabilizing pH.
Still further, the present invention is directed to non-aqueous solutions of metachromatic dye comprising metachromatic dye and non-aqueous solvent, the non-aqueous solution being substantially free of water.
Still further, the present invention is directed to a stabilized metachromatic dye composition for analytical determination of at least one polyionic substance, the metachromatic dye composition including a concentration of metachromatic dye which provides maximum metachromatic absorbance for the at least one polyionic substance when the at least one polyionic substance is present at a concentration of 0. 1 to 1.5 ppm, and the metachromatic dye composition has a percent change in absorbance of less than about 10% when stored for a period of about one week.
Still further, the present invention is directed to a stabilized aqueous solution of metachromatic dye comprising metachromatic dye in an aqueous solvent, the aqueous solution having a metachromatic dye stabilizing pH, and a percent change in absorbance of less than about 10% when stored for a period of about one week.
Still further, the present invention is directed to a metachromatic dye solution for analytical determination of at least one polyionic substance comprising metachromatic dye and non-aqueous solvent, the solution being substantially free of water, said metachromatic dye solution including a concentration of said metachromatic dye which provides maximum metachromatic absorbance for the at least one polyionic substance when said at least one polyionic substance is present at a concentration of 0.1 to 1.5 ppm, and said non-aqueous solvent comprises at least one of methanol, ethanol, butanol, isopropanol, propanol, ethylene glycol, methylcellosolve, hexane, pentane, heptane, toluene, xylene, benzene, dichlorobenzene, acetone, ethyl acetate, diethyl ether, acetonitrile and dimethylsulfoxide.
Still further, the present; invention is directed to a process for analytical determination of at least one polyionic substance in a sample, comprising forming a mixture by mixing a metachromatic dye solution and the sample, the metachromatic dye solution comprising metachromatic dye and non-aqueous solvent, the solution being substantially free of water, and performing an absorbance measurement on the mixture.
Still further, the present invention is directed to a process for producing a stabilized aqueous solution of metachromatic dye, comprising forming a solution of metachromatic dye in aqueous solvent, the metachromatic dye comprising pinacyanol chloride, and the solution having a metachromatic dye stabilizing pH, and the stabilized aqueous solution of metachromic dye having a percent change in absorbance of less than about 10% when stored for a period of about one week.
Still further, the present invention is directed to a process for producing a metachromatic dye solution for analytical determination of at least one polyionic substance, comprising combining metachromatic dye and non-aqueous solvent so as to form a metachromatic dye solution which is substantially free of water, the metachromatic dye comprising pinacyanol chloride, the metachromatic dye solution including a concentration of the metachromatic dye which provides maximum metachromatic absorbance for the at least one polyionic substance when the at least one polyionic substance is present at a concentration of 0.1 to 1.5 ppm, and the non-aqueous solvent comprises at least one of methanol, ethanol, butanol, isopropanol, propanol, ethylene glycol, methylcellosolve, hexane, pentane, heptane, toluene, xylene, benzene, dichlorobenzene, acetone, ethyl acetate, diethyl ether, acetonitrile and dimethylsulfoxide.
Still further, the present invention is directed to a process for producing a metachromatic dye solution, comprising combining metachromatic dye and non-aqueous solvent so as to form a metachromatic dye solution which is substantially free of water, the metachromatic dye comprising pinacyanol chloride, the non-aqueous solvent having a density at 25xc2x0 C. of about 0.95 to 1.2 g/cm3 and comprising a mixture of methanol and ethylene glycol.
The aqueous solution of metachromatic dye can comprise aqueous solvents having a pH of at least about 8, more preferably a pH of at least about 10, and even more preferably a pH of at least about 11. Preferred pH ranges of the aqueous solvents include a pH range of about 8 to 14, even more preferably a pH range of about 11 to 12, and even more preferably a pH range of about 11 to 11.5. The aqueous solution of metachromatic dye can include at least one basic material, such as a buffer, or a material such as at least one of sodium hydroxide, potassium hydroxide and lithium hydroxide, preferably sodium hydroxide. Moreover, the aqueous solution of metachromatic dye can include at least one non-aqueous solvent.
The metachromatic dye can comprise at least one of pinacyanol chloride, crystal violet, methyl green, malachite green, acridin orange, paraosaniline, nile blue A, neutral red, safrin O, methylene blue, methyl red, brilliant green, toluidine blue, new methylene blue, quinalizarin, tetrachrome, brilliant blue G, and mordant black II, and is preferably pinacyanol chloride.
The non-aqueous solvent can comprise at least one of alcohols, methylcellosolve, hexane, pentane, heptane, toluene, xylene, benzene, dichlorobenzene, acetone, ethyl acetate, diethyl ether, acetonitrile, dimethylsulfoxide, preferably at least one of methanol, ethanol, butanol, isopropanol, propanol and ethylene glycol.
The non-aqueous solution of metachromatic dye can include one or more non-aqueous solvents, preferably a mixture of methanol and ethylene glycol having a preferred 25 vol % of methanol to 75 vol % of ethylene glycol, with the non-aqueous solution preferably having a density at 25xc2x0 C. of about 0.95 to 1.2 g/cm3, more preferably about 1 to 1.1 g/cm3, and even more preferably about 1 to 1.05 g/cm3.
The non-aqueous solution of metachromatic dye is preferably free of water.
The non-aqueous solvent preferably comprises high purity solvent.
The solutions of metachromatic dye preferably include at least one oxygen scavenger.
The solutions of metachromatic dye preferably are in the substantial absence of oxygen.
The solutions of metachromatic dye preferably are purged with an inert gas.
The present invention is also directed to containers including therein the solutions of metachromatic dye according to the present invention. The container at least reduces the transmission of light, and preferably prevents the transmission of light.
The present invention is also directed to methods of determining materials, such as polyionic materials, preferably polyionic polymers utilizing the metachromatic dye solutions according to the present invention.